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RIP Routing Fundamentals
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RIP stands for Routing Information Protocol.
RIP is a dynamic, distance vector routing protocol and was developed for
smaller IP based networks. As mentioned earlier, RIP calculates the best route
based on hop count.
There are currently two versions of RIP protocol.
RIPv1: RIP version 1 is among the oldest protocols.
Limitations of RIPv1:
1. Hop Count Limit: Destination that is more than 15 hops away is considered
unreachable by RIPv1.
2. Classful Routing Only: RIP is a classful routing protocol. RIPv1 doesn't
support classless routing. RIP v1 advertises all networks it knows as classful
networks, so it is not possible to subnet a network using RIP v1.
3. Metric limitation: The best route in RIP is determined by counting the
number of hops required to reach the destination. A lower hop count route is
always preferred over a higher hop count route. One disadvantage of using hop
count as metric is that if there is a route with one additional hop, but with
significantly higher bandwidth, the route with smaller bandwidth is taken. This
is illustrated in the figure below:
The RIP routed packets take the path through 56KBPS link since the
destination can be reached in one hop. Though, the alternative provides a
minimum bandwidth of 1MBPS (though using two links of 1MBPS, and 2MBPS each), it
represents 2 hops and not preferred by the RIP protocol.
Features of RIP v2:
RIP v2 is a revised version of its predecessor RIP v1. The following are the
important feature enhancements provided in RIPv2:
1. RIPv2 packets carry the subnet mask in each route entry, making RIPv2 a
classless routing protocol. It provides support for variable-length subnet
masking (VLSM) and classless addressing (CIDR).
2. Next Hop Specification: In RIPv2, each RIP entry includes a space where an
explicit IP address can be entered as the next hop router for datagrams intended
for the network in that entry.
For example, this field can be used when the most efficient route to a
network is through a router that is not running RIP. Since, that a router will
not exchange RIP messages, explicit Next Hop field allows the router to be
selected as the next hop router.
3. Authentication: RIPv1 does not support authentication. This loophole may be
used maliciously by hackers, that may resulting in delivering the data packets
to a fictitious destination as determined by the hacker. RIPv2 provides a basic
authentication scheme, so that a router can accept RIP messages from a neighboring
router only after ascertaining its authenticity.
4. Route Tag: Each RIPv2 entry includes a Route Tag field, where additional
information about a route can be stored. It provides a method for distinguishing
between internal routes (learned by RIP) and external routes (learned from other
Limitations of RIP v2:
One of the biggest limitations of RIPv1 still remains with RIPv2. It is hop
count limitation, and metric. The hop count of 16 still remains as unreachable,
and the metric still remains hop count. A smaller hop count limits the network
diameter, that is the number of routers that can participate in the RIP network.
While the packet travels from source to destination through an
Internetwork, which of the following statements are true? (Choose 2 best
A. The source and destination hardware (interface) addresses change
B. The source and destination hardware (interface) addresses remain
C. The source and destination IP addresses change
D. The source and destination IP addresses remain constant.
Ans. A, D
Explanation: While a packet travels through an
Internetwork, it usually
involves multiple hops. It is important to know that the logical address (IP
address) of the source (that created the packet) and destination (final intended
destination) remain constant, whereas the hardware (interface) addresses change
with each hop.